The present invention relates to beam pumping units and more particularly, walking beam pumping units that are used in producing fluids from wells.
The term beam pumping unit is used to describe a pumping unit in which a walking beam is provided with a bearing support intermediate to its ends. One end of the walking beam is coupled to crank arms by means of pitman arms that are driven by a speed reducer connected to a prime mover to oscillate the walking beam. The other end is provided with a horsehead that is coupled to the polished rod of the well. The downhole pump is connected to the polished rod by means of a rod string. The walking beam reciprocates the connected rod string of the downhole pump to produce fluids from the well. The central bearing of the walking beam is supported by a Samson post which elevates the walking beam to a height sufficient to allow the horsehead to move the polished rod through the complete stroke of the downhole pump.
The height of the pumping unit normally does not create problems in most oilfields since there are no overall height limitations on the pumping unit. There are situations where the height may be an issue, such as irrigated fields, or special shipping and installation requirements where it is desirable to ship the pumping unit assembled. In the case of oilfields located in irrigated agricultural areas, the height of the pumping unit creates problems. This is particularly the case in those irrigated areas that use large sprinkling systems that normally have a clearance under the sprinkling units of approximately 12 ft. or less. Many locations use a sprinkling unit of the type referred to as center pivot irrigation systems in which a long irrigation pipe, for example a 1/4 to 1/2 mile in length, is mounted on elevated wheeled supports. This type of irrigation unit normally has approximately 12 ft. or less of clearance between the irrigation pipe and the ground. Thus, some means are required for lowering the overall height of any pumping units that are located within the irrigated area.
It has been conventional practice when locating pumping units in irrigated areas to dig pits in the irrigated area and mount the pumping unit below the surface of the ground. This will reduce its overall height below the clearance between the irrigation pipe and the ground. While this solves the problem for providing clearance between the pumping unit and the irrigation unit, it introduces the new problem of maintaining the pit free of water. Since many pumping units utilize electric motors and gear type speed reducers to drive the pumping unit, the pit area cannot be flooded. The use of a pit to lower the overall height of the pumping unit also complicates the problem of servicing the pumping unit and well. Pits can also collect debris and hazardous gases, thereby making conditions less safe for personnel.
A possible solution to this problem would be a means to lower the overall height of the pumping unit upon the approach of the irrigation system. Such a system is shown and described in U.S. Pat. Nos. 4,572,012 and 4,788,873. These patents describe a portable beam pumping unit that is trailer mounted and provided with a means for lowering the pumping unit to a height that allows its transport over normal roads. The system described in the above referenced patents requires removal of the mounting means for one leg of the Samson post so that the Samson post can be lowered and thus lower the walking beam. However, when the pumping unit is lowered, the free leg of the Samson post extends below the frame of the pumping unit. An additional problem with the system described in the above patent is that the crank arms used to oscillate the walking beam must be locked in a preset position before the pumping unit can be lowered. This is necessary to prevent the walking beam from contacting other parts of the pumping unit.
The above problems with the prior art render the pumping unit described in the patents unworkable in irrigated fields. For example, the necessity for the rear leg of the Samson post to extend down below the frame of the pumping unit when it is lowered would necessitate the provision of a pit under the pumping unit. Further, the necessity to lock the crank arms in a particular position before lowering the pumping unit and to remove the Samson post mounting means require the attention of a field worker.
Another potential need for a stowable walking beam pumping unit described in the present invention is pre-assembled shipping and simplified installation at the well site. In some remote well locations, pumping unit assembly equipment and trained people might not be easily attainable. In this situation, a pumping unit that could be shipped from the manufacturer in a fully assembled condition would eliminate the need for trained personnel and heavy equipment to rig and assemble the pumping unit at the well site.